jtanman

1982 XR200 smokes, low compression, but rings look good?

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Hi all. I’m helping my neighbor fix his xr200 that hasn’t run for a couple years. When he last had it running he said it smoked really bad. I did a compression test and it produced a measly 50psi.

 

With the smoke/low compression combo I calculated that a simple top end rebuild was in order. But, after getting into it, I noticed that the piston and rings seemed to be in remarkably good shape (at least to my fairly inexperienced eyes). A valve check revealed that the exhaust valve doesn’t seal well, which would help explain the bad compression, but I’m still not sure on the smoking problem. I know valve guides can go bad, but even then it wouldn’t smoke too bad, right? The valves seem to fit quite snugly in the seals as well. My only other thought is that the rings are indeed shot but I just can’t perceive the wear.

 

Anyone thoughts? Should I just go ahead and replace the piston and rings and lap the valves and hope the problem goes away?

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 I'm not an XR200 expert or anything, but if I had an old motor like that all disassembled, I certainly would just go ahead and rebuild it. Having bad valve seals does make the bike smoke badly, just not all the time.

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If it smokes all the time, check for glazed cylinder walls; if it only smokes after cold start, it's valve seals. If cash is short, mike piston and cylinder for clearance: if in spec, and in good shape, just hone cylinder and use old piston with new rings cut to proper end gap. Lap the valves, and if you get a good seal, button it up, cross your fingers and go. Otherwise, head work with recut seats, and fresh valves cut to match.

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3 hours ago, jtanman said:

 

Hi all. I’m helping my neighbor fix his xr200 that hasn’t run for a couple years. When he last had it running he said it smoked really bad. I did a compression test and it produced a measly 50psi.

 

With the smoke/low compression combo I calculated that a simple top end rebuild was in order. But, after getting into it, I noticed that the piston and rings seemed to be in remarkably good shape (at least to my fairly inexperienced eyes). A valve check revealed that the exhaust valve doesn’t seal well, which would help explain the bad compression, but I’m still not sure on the smoking problem. I know valve guides can go bad, but even then it wouldn’t smoke too bad, right? The valves seem to fit quite snugly in the seals as well. My only other thought is that the rings are indeed shot but I just can’t perceive the wear.

 

Anyone thoughts? Should I just go ahead and replace the piston and rings and lap the valves and hope the problem goes away?

 

 

How much ring end gap do you have............?  Is the cyl standard bore or oversize (bored)....? :thinking:

Old School Al

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The 2 valve XR185/200s seldom have valve issues, so checking for leak with a thin liquid like thinner or gas is a good check. Stock valves have a thin hard coating that can be worn thru during lapping.  A quick check for guides is to insert a valve into its guide until the tip is flush with the top of the guide. Then place a finger over the top of the guide and quickly pull the valve out. A popping sound indicates a tight guide.

You can check ring wear by measuring ring end gap when installed in the cylinder, use the piston to square the ring to the bore. Measuring in several places will indicate taper in the bore.  You can also use a feeler gauge to measure piston to bore clearance.  From my experience a worn/tapered  cylinder can cause a lot of smoke even with new rings. Stock bore is  65.5mm and the common next size piston is 66.0mm.

Honda OEM pistons have a cross hatch pattern on the underside of the crown.

These engines can have a long life if maintained but worn to the point of bad smoking and low compression would indicate other possible damage so I recommend replacing the timing chain and chain guides.  They can also seize/damage the bushing on the right end of the cam. Rocker shafts wear but they can be switched for a new wear surface against the rockers.

Buy a new XR200 oil pump, or a CRF230 pump and use the XR drive gear. The late model XR pump supercedes the early pump and has a higher capacity, and no repair parts are avail for the early pump.  

And get a Honda Service Manual.

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On 6/10/2018 at 10:46 AM, jtanman said:

 

Hi all. I’m helping my neighbor fix his xr200 that hasn’t run for a couple years. When he last had it running he said it smoked really bad. I did a compression test and it produced a measly 50psi.

 

With the smoke/low compression combo I calculated that a simple top end rebuild was in order. But, after getting into it, I noticed that the piston and rings seemed to be in remarkably good shape (at least to my fairly inexperienced eyes). A valve check revealed that the exhaust valve doesn’t seal well, which would help explain the bad compression, but I’m still not sure on the smoking problem. I know valve guides can go bad, but even then it wouldn’t smoke too bad, right? The valves seem to fit quite snugly in the seals as well. My only other thought is that the rings are indeed shot but I just can’t perceive the wear.

 

Anyone thoughts? Should I just go ahead and replace the piston and rings and lap the valves and hope the problem goes away?

 

 

On 6/10/2018 at 2:37 PM, Old School Al said:

 

How much ring end gap do you have............?  Is the cyl standard bore or oversize (bored)....? :thinking:

Old School Al

 

Were you able to figure out what you have......................?:excuseme:

Old School Al

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Sorry for the delay, thanks for all of the helpful input! I plan on checking the ring gap after work today. This is my first top end rebuild so any tips and tricks no matter how small are greatly appreciated. I inspected the camshaft yesterday and discovered the lobes to be pretty worn with flat spots so I suppose I'll need to replace that. 

Question- what should I be looking for when I'm checking the ring gaps?

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Posted (edited)

You want to see if the ring end gap is within spec............in this case (excessive smoking) too much end gap.   Also check gap at different places (worn and unworn) in the bore and compare results.  Has the cyl been bored oversize...........?

If the cam lobes are worn, the rockers will be also.  What do the cam bearings look like?

Old School Al

Edited by Old School Al

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Alright, here are the updates and some answers to questions (thanks for all of your input):

I don't think this bike has cam bearings and just rolls around in solid metal bushings (unless that's actually considered a bearing). Anyway, the bushings and cam journals seem to be alright without weird wear or scoring. The rocker arm rollers also seem to be alright, which is surprising considering the shape of the cam lobes. In the pictures that I'll attach it may look like the rollers have flat spots but they are imperceptible to the touch.

As far as whether or not the cylinder is stock or bored, I honestly don't know and unfortunately don't have a micrometer to determine that.

I did the valve guide check method suggested by Chuck and was pleased to hear good pops from both guides as well as decent suction on my fingertip, so I hope to rule out the valve guides as a possible source of escaping oil.

Both of the compression rings had a gap of about .021 and seem to be in good shape as far as I can tell. The oil control rings are less convincing as they barely seemed to hug the cylinder wall at all. The gaps were also considerably wider with at least twice the width of the compression rings. Is that normal?

An inspection of the cylinder wall revealed that it's clearly glazed since the bottom portion that doesn't come in contact with the rings has an obvious cross-hatching while the rest seems to be devoid of such. As Old Plonker mentioned, could this alone be the source of the smoking?

At this point, my tentative plan is as follows:

  • Deglaze cylinder
  • Replace piston rings
  • Lap valves and use gas to ensure the exhaust valve doesn't leak anymore
  • Replace camshaft
  • Replace base, head, and valve cover gaskets
  • Set timing, adjust valves, reassemble, and pray for the best.

Am I missing anything?

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IMG_4348.JPGIMG_4352.JPGIMG_4370.JPGIMG_4358.JPGIMG_4366.JPG

In the photo focused on the cylinder wall you can see the cross hatched section.

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I don't see any mention of timing chain or sprockets. 

Have you pulled the flywheel to see if there is any sign of excessive wear from the chain? 

It is an easy, inexpensive addition since you are already there. Probably needed too based on the other symptoms. 

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Good thinking. I was wondering if I should play it cheap and hope the chain is fine, but you’re probably right. Better safe than sorry.

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Go easy with the valve lapping. @chuck brought up something I didn't know, that the valves have a thin hard coating that can be damaged by lapping. Did you try his suggested test of checking the valve seal with a thin solvent?

Chuck also said that if the bore is worn to a taper, it will smoke even with new rings, so now is the time to check that. If you are shopping out the honing, have them check the bore for you.

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Good call, I’ll have the shop check the bore for me. Thanks for the reminder! I did spray carb cleaner into the valve chambers and the intake valve didn’t leak at all so I was planning on very lightly lapping that one. The exhaust valve leaked pretty badly... do I dare try and lap that one into a good seal or should I just replace the valve?

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I have no idea what makes Chuck think the intake has a hard coating...........multitasking again?;)  Intake valves are soft with no hard coating..............that's why they wear so much!:excuseme: While excessive lapping is not good, you'll wear out before the coating does on the exhaust valve hand lapping.

On valve guide clearance the tried and true method is to lift the valve just off the seat and wiggle the valve in the guide.............the way the guys that have to stand behind their work have done it for years!:thumbsup: 

Old School Al

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17 hours ago, Old School Al said:

I have no idea what makes Chuck think the intake has a hard coating...........multitasking again?;)  Intake valves are soft with no hard coating..............that's why they wear so much!:excuseme: While excessive lapping is not good, you'll wear out before the coating does on the exhaust valve hand lapping.

On valve guide clearance the tried and true method is to lift the valve just off the seat and wiggle the valve in the guide.............the way the guys that have to stand behind their work have done it for years!:thumbsup: 

Old School Al

The  info on valve coating that I posted was provided to me years ago by Powroll, same for the quick method valve guide check. I consider Powroll most authoritative on these small 2 valve engines.

The cylinder heads are very durable so a leaking valve is unusual.

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Posted (edited)

Thanks guys! I enthusiastically lapped the exhaust valve and after reinstalling it I was pleased to find that gas doesn't leak out when poured into the valve chamber (it started to visibly seep after a couple minutes but hey, nothing's perfect right?). Unfortunately the same couldn't be said about the intake valve, which, if you remember, wasn't leaking previously :facepalm:. I did notice while lapping it that there was a small section on the valve just under a centimeter wide that wasn't producing that beautiful gray color of a freshly lapped valve. I also noticed slight cupping. Against better judgement I reinstalled it anyway because I figured if it wasn't leaking before then it should be fine, right? Nope. Now it leaks. 

It was probably due for a replacement anyway I suppose. There's not going to be a problem if I buy a brand new intake valve and lap it is there? I would love to not need to send the head somewhere to get the valve seat cut.

I'm picking up the freshly honed cylinder later today and they'll tell me if they found the cylinder to be tapered or not. Fingers crossed! 

Edited by jtanman

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On 6/14/2018 at 8:20 AM, Chuck. said:

The  info on valve coating that I posted was provided to me years ago by Powroll, same for the quick method valve guide check. I consider Powroll most authoritative on these small 2 valve engines.

The cylinder heads are very durable so a leaking valve is unusual.

 

None of the key people at Powroll would have made statements like that on intake valves for small Honda singles.................total BS!  With all the tech you offer you should know better anyway and have called BS if they had!  I thought we had you up to speed on this after the last time you brought this up on the forum.............?;)

Old School Al

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Am i wrong or does the pick of the cam show that the lobe is worn down with burrs on the outside?

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